I reload 12 & 28 guage. You don't save any money with standard 12ga loads, unless it is heavy or esoteric. Loads around 36-44 gram (1.25-1.5oz in old money) are usually cheaper to load than buy. I do it because I can customise it to do exactly what I like, for example a light clay load I use with a slightly lower velocity than the commercial ones, so I gain the advantage of the lighter load, as I see it, of less recoil.
With 28ga there are savings - the cost of them to buy is scary but there's less powder & shot in them, so are relatively cheap to load.
"Savings" of course ignores the cost of the press etc... like all these things one does it for the satisfaction of shooting things with ones self assembled cartridges - like a trout on a self tied fly or deer with a home load.